Chapter 5: The Working Cell

The molecule most directly involved in energy transfer within cells is _____.

ATP --A molecule called ATP is responsible for fueling most energy-requiring reactions in cells.--

The concentration of calcium in a cell is 0.3%. The concentration of calcium in the surrounding fluid is 0.1%. How could the cell obtain more calcium?

Active Transport --For the cell to accumulate calcium, it must move calcium against its concentration gradient. This process requires energy.--

Which of the following statements concerning enzymes is true and correct?

An enzyme is very specific in terms of which substrates it can bind. --Only the specifically appropriate substrate will cause an induced fit, where the active site snugly binds to the substrate.--

The movement of atoms, ions, or molecules from a region of higher concentration to regions of lower concentration is called _____.

Diffusion --Diffusion is the tendency of molecules to spread out in the available space. A substance will diffuse from an area of high concentration to an area of lower concentration.--

A nursing infant is able to obtain disease-fighting antibodies, which are large protein molecules, from its mother's milk. These molecules probably enter the cells lining the baby's digestive tract via _____.

Endocytosis --Endocytosis is the procedure that cells use to import large molecules across their membranes.--

Which of the following is the best example of a substance that contains chemical energy?

Food that you eat --Our body taps into the chemical energy of ingested foods to do work.--

The diffusion of water across a selectively permeable membrane is called _____.

Osmosis --This is a special case of passive transport.--

Which of the following statements is true about passive transport?

Passive transport requires no expenditure of cellular energy. --Passive transport is an example of diffusion down a concentration gradient, which is a spontaneous characteristic of matter.--

Which one of the following is an example of osmosis?

The movement of a drink of water eventually into the cells lining the small intestine --The passive transport of water across a selectively permeable membrane is called osmosis.--

Calories are units of _____.

energy --Because a calorie represents such a tiny amount of energy, it's conventional to use kilocalorie units.--

The transport of molecules of a particular solute from inside an animal cell across the cell membrane to the extracellular fluid always requires energy when __________.

the concentration of the solute is lower inside the cell than outside it --To pump a molecule across a membrane against its concentration gradient, the cell must expend metabolic energy, which is provided by ATP. This type of membrane traffic is called active transport.--

An enzyme is a protein that __________.

changes the rate of a metabolic reaction without being consumed by the reaction --This permits enzyme molecules to be used repeatedly.--

When in solution, a molecule that moves slowly across an artificial membrane moves rapidly across a plasma membrane. This occurs regardless of whether the concentration of this molecule is higher inside or outside the cell. Using this information, which transport mechanism is most likely to be responsible for the movement of the molecule across a plasma membrane?

Active Transport --Some transport proteins can move molecules against their concentration gradient in a process called active transport.--

Which one of the following statements about energy is correct?

Energy cannot be created or destroyed. --This is a key part of the principle of conservation of energy.--

Which is the best definition of energy?

The capacity to do work

A primary function of the cell membrane is to __________.

regulate the passage of materials into and out of the cell --Transport proteins within the membrane are critical helpers.--